The general aim of the proposed research is to study the trophic interactions between presynaptic and postsynaptic nerve elements. A combination of electrophysiological, neurochemical and histological techniques will be applied in order to evaluate changes in the functional and structural integrity of synapses from the avian ciliary ganglion under various experimental conditions. It is of particular interest to define the influence of the postsynaptic cell on the development and maintenance of a viable presynaptic nerve terminal, and therefore procedures designed to selectively alter postsynaptic activity will be employed. Additional experiments will be conducted in order to characterize the mechnisms by which postsynaptic receptor sensitivity is regulated. Once completed, these studies will contribute to the long range goal of understanding the ways in which the synapse and hence the nervous system can adapt to constantly changing requirements for signal processing.